#pragma once

//
// handler_allocator.cpp
// ~~~~~~~~~~~~~~~~~~~~~
//
// Copyright (c) 2003-2008 Christopher M. Kohlhoff (chris at kohlhoff dot com)
//
// Distributed under the Boost Software License, Version 1.0. (See accompanying
// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
//

#ifndef HANDLER_ALLOCATOR_HPP
#define HANDLER_ALLOCATOR_HPP

#include <boost/aligned_storage.hpp>

// Class to manage the memory to be used for handler-based custom allocation.
// It contains a single block of memory which may be returned for allocation
// requests. If the memory is in use when an allocation request is made, the
// allocator delegates allocation to the global heap.
class handler_allocator
{
public:
	handler_allocator()
		: in_use_(false)
	{
	}

	void* allocate(std::size_t size)
	{
		if (!in_use_ && size < storage_.size)
		{
			in_use_ = true;
			return storage_.address();
		}
		else
		{
			return ::operator new(size);
		}
	}

	void deallocate(void* pointer)
	{
		if (pointer == storage_.address())
		{
			in_use_ = false;
		}
		else
		{
			::operator delete(pointer);
		}
	}

private:
	// Storage space used for handler-based custom memory allocation.
	boost::aligned_storage<1024> storage_;

	// Whether the handler-based custom allocation storage has been used.
	bool in_use_;
};

// Wrapper class template for handler objects to allow handler memory
// allocation to be customised. Calls to operator() are forwarded to the
// encapsulated handler.
template <typename Handler>
class custom_alloc_handler
{
public:
	custom_alloc_handler(handler_allocator& a, Handler h)
		: allocator_(a),
		handler_(h)
	{
	}

	template <typename Arg1>
	void operator()(Arg1 arg1)
	{
		handler_(arg1);
	}

	template <typename Arg1, typename Arg2>
	void operator()(Arg1 arg1, Arg2 arg2)
	{
		handler_(arg1, arg2);
	}

	friend void* asio_handler_allocate(std::size_t size,
		custom_alloc_handler<Handler>* this_handler)
	{
		return this_handler->allocator_.allocate(size);
	}

	friend void asio_handler_deallocate(void* pointer, std::size_t /*size*/,
		custom_alloc_handler<Handler>* this_handler)
	{
		this_handler->allocator_.deallocate(pointer);
	}

private:
	handler_allocator& allocator_;
	Handler handler_;
};

// Helper function to wrap a handler object to add custom allocation.
template <typename Handler>
inline custom_alloc_handler<Handler> make_custom_alloc_handler(
	handler_allocator& a, Handler h)
{
	return custom_alloc_handler<Handler>(a, h);
}

#endif // HANDLER_ALLOCATOR_HPP